In the context of computer graphics, the generation of realistic looking virtual objects takes into account the interaction of light both on the surface of the object and in the volume of the object. Such interactions of light with the object are otherwise referred to as reflection and scattering, respectively. When accounted for, reflection and scattering produce visual effects such as shadowing, masking, interreflection, translucency and fine-scale silhouettes which elevate the realism of rendered images of the object. The interactions of light with the object are physically governed by the shape and material attributes of the object.
Previous attempts to map material attributes (e.g., color, surface normal perturbations, height field displacements, and volumetric geometry) onto surfaces to model fine-scale surface geometry, referred to as mesostructure, and its interaction with illumination, fail to take into consideration various appearance effects that arise from light transport within the material of the object. This deficiency is significant since many materials in the physical world are translucent to some degree. Thus, the appearance of the surface of an object may not be realistic.
On the other hand, further attempts to map material attributes onto surfaces that do account for translucency are beset by problems regarding the computational expense required. That is, detailed renderings of translucent objects by simulating radiance transfer through a participating medium require either an impractical amount of data storage or a significant amount of computation at rendering time.